1. Field of the Invention
This invention relates to an improved furnace fuel optimizer for more effectively controlling fuel consumption in a furnace and a method for using the furnace fuel optimizer. In particular, the furnace fuel optimizer is designed to control combustion air by maintaining a convective section differential pressure value or a convective section heat duty value while monitoring CO emissions in the flue gas and monitoring the draft below the convective section in order to obtain an optimum control value. The optimizer then regulates the furnace to correspond to the optimum control value by adjusting the air input to the furnace so that continuous furnace operation is possible at maximum efficiency.
2. Description of the Prior Art
Furnaces, or process heaters as they are sometimes referred to, are used by industries to elevate the temperature of various fluids and gases by passing these fluids and gases through hollow tubular tubes or coils which are enclosed in the furnace. When the fluid or gas absorbs an adequate amount of heat, it is transferred away to another unit for further processing. In an oil refinery, normally over half of the total fuel consumption is attributable to the firing or heating of such furnaces. Most of this heat is used to generate steam or to heat various feed streams, for example, a crude oil feed stream. Since a large percentage of the fuel actually consumed in a refinery is directly related to these furnaces, it is little wonder that the industry has been trying for years to perfect a control apparatus which will increase efficiency. This task has been compounded by such factors as furnace design and configuration, air leakages, burner placement and burner size. In the past, people have tried to provide control to the furnaces by adjusting the fuel to oxygen ratio. This was feasible to a certain extent because the fuel to oxygen ratio provides a predictable correlation over a wide range of fuel oils and gas compositions when excess air is present. To do this, Orsat analysis using carbon dioxide and oxygen percentages was used to calculate the amount of excess air which should be injected into the furnace. Although this method worked, the results were not very reliable, even when oxygen analyzers replaced the Orsat analysis. The reason for this was that an oxygen reading alone could not quickly compensate for any drastic changes which might occur within the furnace. Two other disadvantages of the oxygen analyzer were: (1) if it was located in the furnace's stack, air in-leakage could result in gross distortions of the true excess oxygen in the flame cloud, and (2) if it was located in the firebox, the oxygen would be measured at one location only, when in actuality, a typical firebox contains varying oxygen levels. To date, no one has devised an air input control scheme which can provide maximum efficiency and thereby more effectively control fuel consumption in the furnace.
An object of this invention is to provide a furnace fuel optimizer which will provide maximum fuel efficiency in a furnace.
Another object of this invention is to provide a furnace fuel optimizer which will more effectively control fuel consumption in a furnace.
A further object of this invention is to provide a method for using the furnace fuel optimizer to minimize excess air and fuel consumption.
Still further, an object of this invention is to reduce the cost of operating a furnace by regulating the amount of combustion air to the furnace.
Other objects and advantages will become apparent to one skilled in the art based upon the ensuing description.